Field of the Invention
The present invention relates to a heat treatment apparatus and a heat treatment method for heating a sheet precision electronic substrate (hereinafter, simply referred to as a “substrate”), such as a semiconductor wafer, by irradiating the substrate with light.
Description of the Background Art
In the process of manufacturing a semiconductor device, the introduction of impurities is an essential step for forming pn junctions in a semiconductor wafer. At present, it is common to introduce impurities by ion implantation and subsequent annealing. Ion implantation is a technique for physically doping impurities by causing impurity elements such as boron (B), arsenic (As), or phosphorus (P) to be ionized and collide with a semiconductor wafer with a high acceleration voltage. The doped impurities are activated by annealing. At this time, if the annealing time becomes about several seconds or longer, the doped impurities are deeply diffused by heat, and as a result, the junction depth may become too deeper than required and hinder the formation of a good device.
In view of this, flash-lamp annealing (FLA) is recently attracting attention as an annealing technique that allows semiconductor wafers to be heated in an extremely short time. Flash-lamp annealing is a heat treatment technique using xenon flash lamps (hereinafter, “flash lamps” simply referred to indicate xenon flash lamps) to irradiate the surface of a semiconductor wafer with flash light so that the temperature of only the surface of the semiconductor wafer that is doped with impurities is raised in an extremely short time (several milliseconds or less).
The radiation spectral distribution of xenon flash lamps ranges from ultraviolet to near-infrared regions, with the xenon flash lamps having shorter wavelengths than conventional halogen lamps, and approximately coincides with the fundamental absorption band of silicon semiconductor wafers. Thus, in the case where flash light is applied from xenon flash lamps to a semiconductor wafer, less light will be transmitted through the semiconductor wafer and therefore it is possible to quickly raise the temperature of the semiconductor wafer. It has also been found that the temperature of only the vicinity of the surface of the semiconductor wafer will selectively be raised with extremely short-time application of flash light for several milliseconds or less. Thus, extremely short-time temperature rise with the xenon flash lamps enables the impurities to be activated simply without being diffused deeply.
As examples of such a heat treatment apparatus using xenon flash lamps, U.S. Pat. No. 4,649,261 and U.S. 2003/0183612 A1 disclose heat treatment apparatuses that achieve desirable heat treatment with a combination of pulsed light-emitting lamps such as flash lamps that are arranged on the front side of a semiconductor wafer and continuous lighting lamps such as halogen lamps that are arranged on the rear side of the semiconductor wafer. In the heat treatment apparatuses disclosed in U.S. Pat. No. 4,649,261 and U.S. 2003/0183612, a semiconductor wafer is preheated to a certain degree of temperature with, for example, halogen lamps, and then the temperature of the semiconductor wafer is raised to a desired treatment temperature by pulse heating with flash lamps.
Some semiconductor wafers treated with flash-lamp annealing contain various types of films such as a resist film. When flash light is applied for heat treatment to this type of semiconductor wafer containing films, an inner wall of a chamber accommodating the semiconductor wafer, and a structure inside the chamber such as a susceptor may be contaminated. It is estimated that this contamination is caused by adhesion of carbon contaminants to the structure inside the chamber at the time of combustion of the respective films on the semiconductor wafer by flash heating.
Contamination of the structure inside the chamber becomes a contamination source for a subsequent semiconductor wafer. During light irradiation, light reflected on an inner wall surface of the chamber is also applied to the semiconductor wafer. When the inner wall surface of the chamber is contaminated, reflectance at the contaminated portion lowers. In this case, in-plane temperature distribution of the semiconductor wafer becomes non-uniform during irradiation of light. This condition influences a treatment result of flash heating treatment, and produces a bend of the semiconductor wafer in correspondence with the non-uniform temperature distribution. Moreover, in the case of the structure which disposes lamps on both surfaces of the semiconductor wafer as disclosed in U.S. Pat. No. 4,649,261 and US2003/0183612, light transmittance lowers when the susceptor is contaminated.